Negative electrode, electrochemical device containing same, and electronic device

ABSTRACT

A negative electrode includes a current collector and a negative active material layer disposed on the current collector. The negative active material layer includes negative active material particles. The negative active material particles include secondary particles. The negative active material layer includes a pore A. A diameter of the pore A is 59 nm to 73 nm when tested by a mercury intrusion porosimetry. A ratio C004/C110 of the negative active material layer is 6 to 20. The electrochemical device using the negative electrode according to this application possesses a relatively high capacity and improved performance of resistance to cycle expansion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International PatentApplication Serial Number PCT/CN2022/075646, filed on Feb. 9, 2022,which claims priority to Chinese Patent Application No. 202110333773.1,filed on Mar. 29, 2021, the contents of each are incorporated herein byreference in their entireties.

TECHNICAL FIELD

This application relates to the field of energy storage, and inparticular, to a negative electrode, an electrochemical devicecontaining same, and an electronic device, especially a lithium-ionbattery.

BACKGROUND

Electrochemical devices (such as a lithium-ion battery) are widely usedby virtue of advantages such as environmental friendliness, a highworking voltage, a high specific capacity, and a long cycle life, andhave become the most promising new green chemical power source in theworld today. A small-sized lithium-ion battery is usually used as apower supply for a portable electronic communications device (forexample, a portable camcorder, a mobile phone, or a notebook computer),especially for a high-performance portable device. In recent years, amedium-sized and large-sized lithium-ion battery characterized by a highoutput voltage has been developed for use in an electric vehicle (EV)and a large-scale energy storage system (ESS). A key technical issue tobe urgently solved that accompanies the wide application of thelithium-ion battery is to improve cycle performance of the battery.Improving an active material in an electrode is one of approaches tosolving the issue.

A main practice in the prior art is to coat and carbonize graphite, andsuppress expansion between particles by using a surface coating layer.By coating, polarization is reduced, and accumulation of side reactionproducts is reduced, thereby mitigating the problem of cycle expansion.However, this practice severely affects an energy density of thelithium-ion battery, and one performance indicator is improved at thecost of another, making it difficult to improve the comprehensiveperformance of the lithium-ion battery in use. In view of this, it isnecessary to provide an improved negative active material, a negativeelectrode made of the negative active material, an electrochemicaldevice, and an electronic device.

SUMMARY

Embodiments of this application provide a negative electrode, anelectrochemical device containing same, and an electronic device in anattempt to solve at least one problem in the related art to at leastsome extent.

In an embodiment, this application provides a negative electrode. Thenegative electrode includes a current collector and a negative activematerial layer disposed on the current collector. The negative activematerial layer includes negative active material particles. The negativeactive material particles include secondary particles. The negativeactive material layer includes a pore A. A diameter of the pore A is 59nm to 73 nm when tested by a mercury intrusion porosimetry. A ratioC004/C110 of the negative active material layer is 6 to 20.

In some embodiments, when tested by the mercury intrusion porosimetry, adifferential mercury intake of the pore A is 0.150 to 0.190 mL/g·μm⁻¹.

In some embodiments, the negative active material layer includes a poreB. When tested by the mercury intrusion porosimetry, a diameter of thepore B is 661.6 nm to 793.3 nm, and a differential mercury intake of thepore B is 0.160 to 0.230 mL/g·μm⁻¹.

In some embodiments, a volume ratio between the pore B and the pore A is0.7:1 to 1.42:1.

In some embodiments, the negative active material particles satisfy atleast one of conditions (a) to (d): (a) D_(v50) of the negative activematerial particles is 7.2 to 21.6 μm; (b) D_(v90) of the negative activematerial particles is 28.4 to 40 μm; (c) D_(n10) of the negative activematerial particles is 1.4 to 9.4 μm; or (d) D_(v90) and D_(n10) of thenegative active material particles satisfy: D_(v90)/D_(n10)≤26.

In some embodiments, a powder particle size of the negative activematerial particles before being pressed is D_(1v50), a powder particlesize of the negative active material particles after being pressed undera pressure of 1 ton is D_(2v50), and(D_(1v50)−D_(2v50))/D_(1v50)×100%≤25%.

In some embodiments, a specific surface area of the negative activematerial particles is 0.8 to 2.0 m²/g.

In some embodiments, a specific surface area of the negative activematerial particles before being pressed is B₁, a specific surface areaof the negative active material particles after being pressed under apressure of 1 ton is B₂, and (B₂−B₁)/B₁×100%≤140%.

In another embodiment, this application provides an electrochemicaldevice. The electrochemical device includes the negative electrodeaccording to the embodiments of this application.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, a specific surface area of the negative active materialparticles is 1.9 to 2.4 m²/g.

In some embodiments, when the electrochemical device is charged to avoltage of 4.45 V, as tested by a differential scanning calorimetry(DSC), a maximum exothermic peak of the negative active material layeris 280 to 330° C.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, a powder particle size of negative active materialparticles is D_(av50), a powder particle size of the negative activematerial particles after being pressed under a pressure of 1 ton isD_(bv50), and (D_(av50)−D_(bv50))/D_(av50)×100%≤2%.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, a specific surface area of the negative active materialparticles before being pressed is B₁₁, a specific surface area of thenegative active material particles after being pressed under a pressureof 1 ton is B₂₂, and (B₂₂−B₁₁)/B₁₁×100%≤40%.

In another embodiment, this application provides an electronic device.The electronic device includes the electrochemical device according tothe embodiments of this application.

This application improves the capacity of the lithium-ion battery andthe performance of resistance to cycle expansion of the lithium-ionbattery by optimizing an ontological structure of the negative activematerial particles and the degree of compounding between the negativeactive material particles.

Additional aspects and advantages of the embodiments of this applicationwill be described and illustrated in part later herein or expoundedthrough implementation of the embodiments of this application.

BRIEF DESCRIPTION OF DRAWINGS

For ease of describing the embodiments of this application, thefollowing outlines the drawings needed for describing the embodiments ofthis application. Evidently, the drawings outlined below are merely apart of embodiments in this application. Without making any creativeefforts, a person skilled in the art can still obtain the drawings ofother embodiments according to the structures illustrated in thesedrawings.

FIGURE shows a differential mercury intake curve of a negative activematerial layer according to Embodiment 11 and Comparative Embodiment 1of this application.

DETAILED DESCRIPTION

Embodiments of this application will be described in detail below. Theembodiments of this application are not to be construed as a limitationon this application.

In this application, D_(v50) is a particle size of the negative activematerial measured when the cumulative volume percentage of the negativeactive material particles reaches 50% in a volume-based particle sizedistribution by starting from small-diameter particles, as measured inμm; D_(v90) is a particle size of the negative active material measuredwhen the cumulative volume percentage of the negative active materialparticles reaches 90% in a volume-based particle size distribution bystarting from small-diameter particles, as measured in μm; and D_(n10)is a particle size of the negative active material measured when thecumulative number percentage of the negative active material particlesreaches 10% in a number-based particle size distribution by startingfrom small-diameter particles, as measured in μm.

In addition, a quantity, a ratio, or another numerical value herein issometimes expressed in the format of a range. Understandably, the formatof a range is for convenience and brevity, and needs to be flexiblyunderstood to include not only the numerical values explicitly specifiedand defined in the range, but also all individual numerical values orsub-ranges covered in the range as if each individual numerical valueand each sub-range were explicitly specified.

In the description of specific embodiments and claims, a list of itemsreferred to by using the terms such as “one of”, “one thereof”, “onetype of” or other similar terms may mean any one of the listed items.For example, if items A and B are listed, the phrase “one of A and B”means A alone, or B alone. In another example, if items A, B, and C arelisted, then the phrases “one of A, B, and C” and “one of A, B, or C”mean: A alone; B alone; or C alone. The item A may include a singleelement or a plurality of elements. The item B may include a singleelement or a plurality of elements. The item C may include a singleelement or a plurality of elements.

In the embodiments and claims, a list of items referred to by using theterms such as “at least one of”, “at least one thereof”, “at least onetype of” or other similar terms may mean any combination of the listeditems. For example, if items A and B are listed, the phrases “at leastone of A and B” and “at least one of A or B” mean: A alone; B alone; orboth A and B. In another example, if items A, B, and C are listed, thephrases “at least one of A, B, and C” and “at least one of A, B, or C”mean: A alone; B alone; C alone; A and B (excluding C); A and C(excluding B); B and C (excluding A); or all of A, B, and C. The item Amay include a single element or a plurality of elements. The item B mayinclude a single element or a plurality of elements. The item C mayinclude a single element or a plurality of elements.

Electrochemical Device

In an embodiment, this application provides an electrochemical device.The electrochemical device includes a positive electrode, a negativeelectrode, a separator, and an electrolytic solution.

In some embodiments, the electrochemical device according to thisapplication includes, but is not limited to: a primary battery or asecondary battery.

In some embodiments, the electrochemical device is a lithium secondarybattery.

In some embodiments, the lithium secondary battery includes, but is notlimited to, a lithium metal secondary battery, a lithium-ion secondarybattery, a lithium polymer secondary battery, or a lithium-ion polymersecondary battery.

1. Negative Electrode

An embodiment of this application provides a negative electrode. Thenegative electrode includes a current collector and a negative activematerial layer disposed on the current collector. The negative activematerial layer includes negative active material particles. The negativeactive material particles include secondary particles. The negativeactive material layer includes a pore A. A diameter of the pore A is 59nm to 73 nm when tested by a mercury intrusion porosimetry. A ratioC004/C110 of the negative active material layer is 6 to 20.

In some embodiments, the diameter of the pore A is 59 nm, 60 nm, 61 nm,62 nm, 63 nm, 64 nm, 65 nm, 66 nm, 67 nm, 68 nm, 69 nm, 70 nm, 71 nm, 73nm, or a range formed by any two thereof.

In some embodiments, the ratio C004/C110 of the negative active materiallayer is 6, 8, 10, 12, 14, 16, 18, or 20, or a range formed by any twothereof.

In some embodiments, when tested by the mercury intrusion porosimetry, adifferential mercury intake of the pore A is 0.150 to 0.190 mL/g·μm⁻¹.

In some embodiments, the differential mercury intake of the pore A is0.150 mL/g·μm⁻¹, 0.160 mL/g·μm⁻¹, 0.170 mL/g·μm⁻¹, 0.180 mL/g·μm⁻¹,0.190 mL/g·μm⁻¹, or a range formed by any two thereof.

In some embodiments, the negative active material layer includes a poreB. When tested by the mercury intrusion porosimetry, a diameter of thepore B is 660 nm to 800 nm, and a differential mercury intake of thepore B is 0.160 to 0.230 mL/g·μm⁻¹.

In some embodiments, the diameter of the pore B is 660 nm, 670 nm, 680nm, 690 nm, 700 nm, 710 nm, 720 nm, 730 nm, 740 nm, 750 nm, 760 nm, 770nm, 780 nm, 790 nm, 790 nm, 800 nm, or a range formed by any twothereof.

In some embodiments, a volume ratio between the pore B and the pore A is0.7:1 to 1.42:1. In some embodiments, the volume ratio between the poreB and the pore A is 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1,1.4:1, 1.42:1, or a range formed by any two thereof. When the volumeratio between the pore B and the pore A falls within the above range,the area of exposure of the negative active material exposed to theelectrolytic solution can be controlled, side reactions can be reduced,and decrease of a first-cycle Coulombic efficiency is avoided. Inaddition, high fluidity and infiltration effects of the electrolyticsolution can be ensured, and increase of impedance can be avoided.

In some embodiments, the negative active material particles satisfy atleast one of conditions (a) to (d): (a) D_(v50) of the negative activematerial particles is 7.2 to 21.6 μm; (b) D_(v90) of the negative activematerial particles is 28.4 to 40.0 μm; (c) D_(n10) of the negativeactive material particles is 1.4 to 9.4 μm; or (d) D_(v90) and D_(n10)of the negative active material particles satisfy: D_(v90)/D_(n10)≤26.

In some embodiments, D_(v50) of the negative active material particlesis 7.2 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21.6 μm, or arange formed by any two thereof.

In some embodiments, Do of the negative active material particles is28.4 μm, 30 μm, 32 μm, 34 μm, 35.7 μm, 38 μm, 40 μm, or a range formedby any two thereof.

In some embodiments, D_(n10) of the negative active material particlesis 1.4 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.4μm, or a range formed by any two thereof.

In some embodiments, the ratio D_(v90)/D_(n10) is 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, or a range formed by any two thereof.

In some embodiments, a powder particle size of the negative activematerial particles before being pressed is D_(1v50), a powder particlesize of the negative active material particles after being pressed undera pressure of 1 ton is D_(2v50), and(D_(1v50)−D_(2v50))/D_(1v50)×100%≤25%.

In some embodiments, the value of (D_(1v50)−D_(2v50))/D_(1v50)×100% is1%, 3%, 6%, 9%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, or a rangeformed by any two thereof. When the value of(D_(1v50)−D_(2v50))/D_(1v50)×100% falls within the above range, thebonding strength of the negative active material particles is relativelyhigh, the particles are more stable during cycles of the electrochemicaldevice, and the expansion rate of the electrochemical device is reduced.

In some embodiments, the specific surface area of the negative activematerial particles is 0.8 to 2.0 m²% g. In some embodiments, thespecific surface area of the negative active material particles is 0.8m²/g, 0.9 m²/g, 1.0 m²/g, 1.1 m²/g, 1.2 m²/g, 1.3 m²/g, 1.4 m²/g, 1.6m²/g, 1.7 m²/g, 1.8 m²/g, 2.0 m²/g, or a range formed by any twothereof.

In some embodiments, the specific surface area of the negative activematerial particles before being pressed is B₁, the specific surface areaof the negative active material particles after being pressed under apressure of 1 ton is B₂, and (B₂−B₁)/B₁×100%≤140%. In some embodiments,the value of (B₂−B₁)/B₁×100% is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,90%, 100%, 110%, 120%, 130%, 140%, or a range formed by any two thereof.When the value of (B₂−B₁)/B₁−100% falls within the above range, the sidereactions of the electrochemical device are reduced, and the expansionrate is reduced.

In some embodiments, the negative active material is graphite particles.In some embodiments, the negative active material includes primarygraphite particles and secondary graphite particles. In someembodiments, the pore A is a packing void between primary graphiteparticles in the secondary graphite particles. In some embodiments, thepore B is mainly a void caused by the packing of the secondary graphiteparticles.

In some embodiments, the secondary graphite particles are prepared fromprimary graphite particles and a binder. In some embodiments, the binderincludes, but is not limited to: low-temperature asphalt,medium-temperature asphalt, high-temperature asphalt, or resin.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, the specific surface area of the negative activematerial is 1.9 to 2.4 m²/g. In some embodiments, when theelectrochemical device is discharged to a voltage of 3 V, the specificsurface area of the negative active material is 1.9 m²/g, 2.0 m²/g, 2.1m²/g, 2.2 m²/g, 2.3 m²/g, 2.4 m²/g, or a range formed by any twothereof.

In some embodiments, when the electrochemical device is charged to avoltage of 4.45 V, as tested by a differential scanning calorimetry(DSC), a maximum exothermic peak of the negative active material layeris 280 to 330° C. In some embodiments, when the electrochemical deviceis charged to a voltage of 4.45 V, as tested by the DSC, the maximumexothermic peak of the negative active material layer is 280° C., 286°C., 290° C., 296° C., 300° C., 306° C., 312° C., 318° C., 322° C., 326°C., 328° C., 330° C., or a range formed by any two thereof.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, a powder particle size of negative active materialparticles is D_(av50), a powder particle size of the negative activematerial after being pressed under a pressure of 1 ton is D_(bv50), and(D_(av50)−D_(bv50))/D_(av50)×100%≤2%.

In some embodiments, the value of (D_(av50)−D_(bv50))/D_(av50)×100% is0.2%, 0.4%, 0.6%, 0.8%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or a range formed byany two thereof.

In some embodiments, when the electrochemical device is discharged to avoltage of 3 V, the specific surface area of the negative activematerial particles before being pressed is B₁₁, the specific surfacearea of the negative active material particles after being pressed undera pressure of 1 ton is B₂₂, and (B₂₂−B₁₁)/B₁₁×100%≤40%. In someembodiments, the value of (B₂₂−B₁₁)/B₁₁×100% is 4%, 8%, 10%, 12%, 16%,18%, 20%, 24%, 28%, 32%, 34%, 36%, 38%, 40%, or a range formed by anytwo thereof.

In some embodiments, the electrochemical device includes a lithium-ionbattery. After undergoing 500 cycles at 25° C., the lithium-ion batteryachieves an expansion rate lower than 9%. In some embodiments, theexpansion rate of the lithium-ion battery is less than 8% or less than7%.

In some embodiments, the negative active material layer further includesa binder. In some embodiments, the binder includes, but is not limitedto: polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethylcellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinylchloride, carboxylated polyvinyl chloride, polyvinyl fluoride,polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,poly(1,1-difluoroethylene), polyethylene, polypropylene,styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin,or nylon.

In some embodiments, the negative active material layer includes aconductive material. In some embodiments, the conductive materialincludes, but is not limited to: natural graphite, artificial graphite,carbon black, acetylene black, Ketjen black, carbon fiber, metal powder,metal fiber, copper, nickel, aluminum, silver, or a polyphenylenederivative.

In some embodiments, the current collector includes, but is not limitedto: a copper foil, a nickel foil, a stainless steel foil, a titaniumfoil, foamed nickel, foamed copper, or a polymer substrate coated with aconductive metal.

In some embodiments, the negative electrode may be obtained by thefollowing method: mixing an active material, a conductive material, anda binder in a solvent to prepare an active material composite, andcoating the active material composite onto the current collector.

In some embodiments, the solvent may include, but is not limited toN-methyl-pyrrolidone.

II. Positive Electrode

The material, composition, and manufacturing method of the positiveelectrode that are applicable to the embodiments of this applicationinclude any technology disclosed in the prior art.

In some embodiments, the positive electrode includes a current collectorand a positive active material layer disposed on the current collector.

In some embodiments, the positive active material includes, but is notlimited to, lithium cobalt oxide (LiCoO₂), a lithiumnickel-cobalt-manganese (NCM) ternary material, lithium ferrousphosphate (LiFePO₄), or lithium manganese oxide (LiMn₂O₄).

In some embodiments, the positive active material layer further includesa binder, and optionally includes a conductive material. The binderimproves bonding between particles of the positive active material andbonding between the positive active material and a current collector.

In some embodiments, the binder includes, but is not limited to:polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose,polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride,polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,poly(1,1-difluoroethylene), polyethylene, polypropylene,styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin,nylon, or the like.

In some embodiments, the conductive material includes, but is notlimited to, a carbon-based material, a metal-based material, aconductive polymer, and a mixture thereof. In some embodiments, thecarbon-based material is selected from natural graphite, artificialgraphite, carbon black, acetylene black, Ketjen black, carbon fiber, orany combination thereof. In some embodiments, the metal-based materialis selected from metal powder, metal fiber, copper, nickel, aluminum, orsilver. In some embodiments, the conductive polymer is a polyphenylenederivative.

In some embodiments, the current collector may include, but is notlimited to aluminum.

The positive electrode may be prepared according to a preparation methodknown in the art. For example, the positive electrode may be obtained bythe following method: mixing an active material, a conductive material,and a binder in a solvent to prepare an active material composite, andcoating the active material composite onto the current collector. Insome embodiments, the solvent may include, but is not limited toN-methyl-pyrrolidone.

III. Electrolytic Solution

The electrolytic solution applicable to the embodiments of thisapplication may be an electrolytic solution known in the prior art.

In some embodiments, the electrolytic solution includes an organicsolvent, a lithium salt, and an additive. The organic solvent of theelectrolytic solution according to this application may be any organicsolvent known in the prior art that can be used as a solvent of theelectrolytic solution. An electrolyte used in the electrolytic solutionaccording to this application is not limited, and may be any electrolyteknown in the prior art. The additive of the electrolytic solutionaccording to this application may be any additive known in the prior artthat can be used as an additive of the electrolytic solution.

In some embodiments, the organic solvent includes, but is not limitedto: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate(DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylenecarbonate, or ethyl propionate.

In some embodiments, the lithium salt includes at least one of anorganic lithium salt or an inorganic lithium salt.

In some embodiments, the lithium salt includes, but is not limited to:lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄),lithium difluorophosphate (LiPO₂F₂), lithiumbistrifluoromethanesulfonimide LiN (CF₃SO₂)₂ (LiTFSI), lithiumbis(fluorosulfonyl)imide Li(N(SO₂F)₂) (LiFSI), lithium bis(oxalate)borate LiB(C₂O₄)₂ (LiBOB), or lithium difluoro(oxalate)borateLiBF₂(C₂O₄) (LiDFOB).

In some embodiments, a concentration of the lithium salt in theelectrolytic solution is 0.5 to 3 mol/L, 0.5 to 2 mol/L, or 0.8 to 1.5mol/L.

IV. Separator

In some embodiments, a separator is disposed between the positiveelectrode and the negative electrode to prevent short circuit. Thematerial and the shape of the separator applicable to an embodiment ofthis application are not particularly limited, and may be based on anytechnology disclosed in the prior art. In some embodiments, theseparator includes a polymer or an inorganic compound or the like formedfrom a material that is stable to the electrolytic solution according tothis application.

For example, the separator may include a substrate layer and a surfacetreatment layer. The substrate layer is a non-woven fabric, film orcomposite film, which, in each case, have a porous structure. Thematerial of the substrate layer is selected from at least one ofpolyethylene, polypropylene, polyethylene terephthalate, and polyimide.Specifically, the material of the substrate layer may be a polypropyleneporous film, a polyethylene porous film, a polypropylene non-wovenfabric, a polyethylene non-woven fabric, or apolypropylene-polyethylene-polypropylene porous composite film.

The surface treatment layer is disposed on at least one surface of thesubstrate layer. The surface treatment layer may be a polymer layer oran inorganic compound layer, or a layer formed by mixing a polymer andan inorganic compound.

The inorganic compound layer includes inorganic particles and a binder.The inorganic particles are selected from a combination of one or moreof alumina, silicon oxide, magnesium oxide, titanium oxide, hafniumdioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide,zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminumhydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.The binder is selected from a combination of one or more ofpolyvinylidene fluoride, poly(vinylidenefluoride-co-hexafluoropropylene), polyamide, polyacrylonitrile,polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone,polyvinyl ether, poly methyl methacrylate, polytetrafluoroethylene, andpolyhexafluoropropylene.

The polymer layer includes a polymer, and the material of the polymer isselected from at least one of a polyamide, a polyacrylonitrile, anacrylate polymer, a polyacrylic acid, a polyacrylate, apolyvinylpyrrolidone, a polyvinyl ether, a polyvinylidene fluoride, or apoly(vinylidene fluoride-hexafluoropropylene).

Electronic Device

The electronic device according to this application may be any devicethat uses the electrochemical device according to the embodiment of thisapplication.

In some embodiments, the electronic device includes, but is not limitedto, a notebook computer, a pen-inputting computer, a mobile computer, ane-book player, a portable phone, a portable fax machine, a portablephotocopier, a portable printer, a stereo headset, a video recorder, aliquid crystal display television set, a handheld cleaner, a portable CDplayer, a mini CD-ROM, a transceiver, an electronic notepad, acalculator, a memory card, a portable voice recorder, a radio, a backuppower supply, a motor, a car, a motorcycle, a power-assisted bicycle, abicycle, a lighting appliance, a toy, a game console, a watch, a powertool, a flashlight, a camera, a large household battery, a lithium-ioncapacitor, or the like.

The following describes preparation of a lithium-ion battery as anexample with reference to specific embodiments. A person skilled in theart understands that the preparation method described in thisapplication are merely examples. Any other appropriate preparationmethods fall within the scope of this application.

Embodiments

The following describes performance evaluation of the lithium-ionbatteries according to the embodiments and comparative embodiments ofthis application.

I. Preparing a Lithium-Ion Battery

1. Preparing a Negative Electrode

1) Preparing a Negative Active Material

a) Using petroleum coke as a raw material (that is, a graphiteprecursor), evenly mixing, at a specified ratio, the petroleum coke withhigh-temperature asphalt serving as a binder, and then feeding themixture into a horizontal vessel, heating up to a temperature of 460° C.to 550° C., and keeping the temperature for 3 hours to obtain agranulated semi-manufacture; and b) then performing high-temperaturegraphitization treatment, where the graphitization temperature is 2500°C. to 3200° C. and the graphitization time is 10 to 200 hours, so as toobtain a graphite negative active material. Table 1 shows specificprocess parameters.

2) Preparing a Negative Electrode

Dispersing the prepared graphite negative active material, styrenebutadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) indeionized water at a weight ratio of 97.7:1.2:1.1, and stirringthoroughly and mixing evenly to obtain a negative slurry. Coating acopper foil with acetylene black to obtain a negative current collector.Coating the negative current collector with the negative slurry, andperforming drying and cold pressing to obtain a negative electrode.

Graphite particles of different diameters may be obtained by crushingand grading the raw material based on any known technique.

2. Preparing a Positive Electrode

Stirring and mixing lithium cobalt oxide (LiCoO₂), acetylene black, andpolyvinylidene difluoride (PVDF) at a weight ratio of 96:2:2 in anappropriate amount of N-methylpyrrolidone (NMP) thoroughly to form ahomogeneous positive slurry, coating a positive current collectoraluminum foil with the slurry, and performing drying and cold pressingto obtain a positive electrode.

3. Preparing an Electrolytic Solution

Mixing ethylene carbonate (EC), propylene carbonate (PC), and diethylcarbonate (DEC) at a weight ratio of 1:1:1 in a dry argon environment,adding LiPF₆, and mixing evenly. Adding 3 wt % fluoroethylene carbonateand 2 wt % adiponitrile, and mixing evenly to obtain an electrolyticsolution, where the concentration of LiPF₆ is 1.15 mol/L.

4. Preparing a Separator

Using a 12 μm-thick polyethylene (PE) porous polymer film as aseparator.

5. Preparing a Lithium-Ion Battery

Stacking the positive electrode, the separator, and the negativeelectrode sequentially, placing the separator between positive electrodeand the negative electrode to serve a separation function, and windingthem to obtain a bare cell; welding tabs and then putting the bare cellinto an outer package made of an aluminum laminated film foil, andinjecting the prepared electrolytic solution into the dried bare cell,and performing steps such as vacuum packaging, standing, chemicalformation, reshaping, and capacity test to obtain a lithium-ion battery.

II. Test Methods

1. Method for Testing Pore Size Distribution of the Negative ActiveMaterial Layer (Mercury Intrusion Porosimetry)

Measuring the pore size distribution of the negative active materiallayer by using a MicroActive AutoPore V9600, which is an automaticmercury intrusion porosimeter: Discharging a battery to a voltage of 3V, disassembling the battery, and taking out the negative electrode, andimmersing the negative electrode in a dimethyl carbonate solution for 5hours, and then drying the negative electrode (containing a negativeactive material layer and a current collector), and then loading thenegative electrode into a dilatometer. Sealing the dilatometer and thenputting it together with the negative electrode into a mercuryporosimeter to test the pore diameter distribution and the pore volumeof the negative active layer.

FIGURE shows a differential mercury intake curve according to Embodiment11 and Comparative Embodiment 1 of this application. The horizontalcoordinate corresponding to the peak in FIGURE represents a porediameter distribution range, and the area of the peak represents thevolume of pores per unit mass of material. The pore diameterscorresponding to two highest peak values are selected herein torepresent the diameters of pores A and B respectively. The pore A issmaller than the pore B in diameter.

2. Method for Testing an Orientation Index (OI) Value

Testing the OI value of the negative active material layer by using anX-ray diffractometer (XRD): Putting a negative electrode sample in theXRD diffractometer, and measuring crystal plane areas of the 004 peakand the 110 peak, denoted by C004 and C110, respectively. Calculatingthe OI value based on the following formula:

OI value=C004/C110

3. Method for Measuring the Particle Size of the Negative ActiveMaterial

Measuring the particle size of the negative active material by using aMalvern particle size analyzer: Dispersing a sample of the negativeactive material in ethanol serving as a dispersant, ultrasonicating thesample for 30 minutes, and then adding the sample into the Malvernparticle size analyzer to measure D_(v50), D_(n10), and D_(v90) of thenegative active material.

4. Method for Measuring the Specific Surface Area of the Negative ActiveMaterial

Measuring the specific surface area of the negative active material bymeans of nitrogen adsorption/desorption by using a specific surface areaanalyzer (Tristar II 3020M): Drying a sample of the negative activematerial in a vacuum drying oven, and then loading the sample into asample tube and measuring the specific surface area in the analyzer.

5. DSC Test Method

Charging a lithium-ion battery to a voltage of 4.45 V, and thendisassembling the battery. Drying the negative electrode, and scrapingoff the negative active material layer. Heating up the negative activematerial layer to 800° C. at a speed of 10° C./min under an N2atmosphere by using a synchronous thermal analyzer (STA 449F3), andtesting the DSC exothermic curve of the material.

6. Method for Testing the Gram Capacity of the Lithium-Ion Battery

Discharging the lithium-ion battery at a current of 0.05 C to a voltageof 5.0 mV, and discharging the battery at a current of 50 μA to avoltage of 5.0 mV. Discharging the battery at a current of 10 μA to avoltage of 5.0 mV, and charging the battery at a current of 0.1 C to avoltage of 2.0 V. Recording the capacity of the lithium-ion battery atthis moment as a gram capacity, 0.05 C is a current value that is 0.05times the nominal gram capacity, and 0.1 C is a current value that is0.1 times the nominal gram capacity.

7. Method for Testing the Cycle Thickness Expansion Rate of theLithium-Ion Battery

Measuring the thickness of the lithium-ion battery at a voltage of 3.95V under a temperature of 25° C., and denoting the thickness as H₀.Charging and discharging the lithium-ion battery at a current rate of1.5 C for 500 cycles, during which the thickness of the lithium-ionbattery at a voltage of 4.45 V is measured at the end of every 50cycles, where the thickness is denoted as H_(n). Calculating the cyclethickness expansion rate of the lithium-ion battery based on thefollowing formula:

Cycle thickness expansion rate at the end of the corresponding number ofcycles=(H _(n) −H ₀)/H ₀×100%.

III. Test Results

Table 1 shows process parameters of the prepared negative activematerial. The weight percent of the binder is a ratio of the weight ofthe binder to the weight of graphite.

TABLE 1 Weight D_(v50) of Heating Heating Graphitization Graphitizationpercent of petroleum temperature time temperature time binder coke instep a) in step a) in step b) in step b) Serial number (%) (μm) (° C.)(hour) (° C.) (hour) Embodiment 1 5 6 500 3 3000 150 Embodiment 2 5 7500 3 3000 150 Embodiment 3 5 8 500 3 3000 150 Embodiment 4 5 9 500 33000 150 Embodiment 5 8 6 500 3 3000 150 Embodiment 6 8 7 500 3 3000 150Embodiment 7 8 8 500 3 3000 150 Embodiment 8 8 9 500 3 3000 150Embodiment 9 11 6 500 3 3000 150 Embodiment 10 11 7 500 3 3000 150Embodiment 11 11 8 500 3 3000 150 Embodiment 12 11 9 500 3 3000 150Embodiment 13 14 6 500 3 3000 150 Embodiment 14 14 7 500 3 3000 150Embodiment 15 14 8 500 3 3000 150 Embodiment 16 14 9 500 3 3000 150Comparative 0 8 500 3 3000 150 Embodiment 1 Comparative 20 8 500 3 3000150 Embodiment 2

Table 2 shows results of the relevant performance test. The DSCexothermic peak temperature means the DSC exothermic peak temperature ofthe negative active material layer when the lithium-ion battery ischarged to a voltage of 4.45 V, and is used to represent the thermalstability of the negative electrode material.

TABLE 2 Volume Differential Differential ratio DSC D_(v50) of mercurymercury between exothermic graphite Diameter of intake of Diameter ofintake of pore B Ratio peak Gram particles pore A pore A pore B pore Band C004/ temperature capacity Expansion Serial number (μm) (nm) (mL/g ·μm⁻¹) (nm) (mL/g · μm⁻¹) pore A C110 (° C.) (mAh/g) rate Embodiment 17.2 59.6 0.150 690.2 0.172 1.15 16 330 353 8.2% Embodiment 2 8.7 63.50.152 688.2 0.17 1.13 18 327 355 8.4% Embodiment 3 10.1 67.2 0.155 670.80.164 1.06 19 325 356 8.6% Embodiment 4 11.2 69.6 0.160 661.6 0.16 1.0420 326 358 8.9% Embodiment 5 9.0 60.0 0.156 711.5 0.183 1.17 13 312 3527.8% Embodiment 6 10.4 64.4 0.160 704.9 0.178 1.12 14 309 354 8.0%Embodiment 7 12.2 68.2 0.167 696.1 0.174 1.07 16 310 355 8.3% Embodiment8 13.4 70.5 0.171 682.7 0.167 0.99 17 306 356 8.4% Embodiment 9 12.061.0 0.163 759.9 0.212 1.25 9 291 351 6.6% Embodiment 10 14.2 65.2 0.170744.3 0.203 1.22 10 290 352 6.9% Embodiment 11 17.5 68.8 0.178 731.70.196 1.11 11 288 353 7.0% Embodiment 12 19.8 71.6 0.184 720.6 0.1881.02 12 289 354 7.2% Embodiment 13 14.5 61.5 0.169 791.3 0.23 1.42 6 285348 6.8% Embodiment 14 18.9 69.1 0.178 779.2 0.225 1.26 7 286 349 6.9%Embodiment 15 20.5 70.1 0.185 768.8 0.221 1.19 8 282 351 7.0% Embodiment16 21.6 72.9 0.190 757.4 0.214 1.17 9 280 352 7.2% Comparative 8.0 65.10.145 501.8 0.106 0.70 21 349 358 9.5% Embodiment | Comparative 25.075.0 0.194 832.5 0.255 1.36 6 267 346 6.7% Embodiment 2

As can be seen from Embodiments 1, 5, 9, and 13, Embodiments 2, 6, 10,and 14, Embodiments 3, 7, 11, and 15, and Embodiments 4, 8, 12, and 16,in preparing the negative active material, when D_(v50) of the graphiteprecursor petroleum coke remains constant, with the increase of theweight percent of the high-viscosity binder, D_(v50) of the graphiteparticles of the negative active material increases; the diameter of thepore A remains basically unchanged, and the differential mercury intakeof the pore A increases; and both the diameter and the differentialmercury intake of the pore B increase. That may be because the porosityof the pore A represents the packing void between primary particles inthe secondary particles, and the porosity of the pore B mainlyrepresents the void caused by the packing of the secondary particles.When the diameter of the primary particles is constant, the size of thepacking void of the primary particles remains unchanged, and therefore,the diameter of the pore A is basically unchanged. When the content ofthe binder increases and more primary particles are compounded in thesecondary particles, there are more voids, and the differential mercuryintake of the pore A increases. The compounding stability of thesecondary particles increases, the particle size increases, the voidsbetween the particles enlarge, and the number of voids also increases.Accordingly, the diameter and the differential mercury intake of thepore B also increase. After the content of the binder increases, theexpansion between particles can be suppressed mutually, and the cyclethickness expansion rate of the lithium-ion battery becomes lower.However, as can be seen from Comparative Embodiment 2, the excessivelyhigh content of the binder reduces the gram capacity of the negativeactive material and affects the energy density of the negative activematerial.

As shown in Comparative Embodiment 1, no high-viscosity binder is addedin preparing the negative active material. The negative active materialis primary particles, which are not compounded to form secondaryparticles. Therefore, after cold pressing, the particles in the negativeactive material layer are arranged in the same orientation and verycompactly, the diameter of the pore B is relatively small, and thedifferential mercury intake is small. Consequently, the cycle thicknessexpansion rate of the lithium-ion battery is relatively high, and theoverall performance is relatively low. As shown in ComparativeEmbodiment 2, a relatively large amount of high-viscosity binder isadded in preparing the negative active material, the degree ofcompounding between particles is high, and the particle arrangement inthe negative electrode film is isotropic. In addition, the diameter ofthe pore B between particles is relatively large, the differentialmercury intake is large, and the cycle thickness expansion rate of thelithium-ion battery is relatively low. However, the relatively lowperformance of lithium storage of the binder affects the gram capacityof the negative active material. In addition, the relatively largediameter of the secondary particles affects the processing performance.

As can be seen from Embodiments 1 to 4. Embodiments 5 to 8. Embodiments9 to 12, and Embodiments 13 to 16, when the content of thehigh-viscosity binder is constant, with the increase of D_(v50) of thepetroleum coke serving as the precursor of the negative active material,the diameter and the differential mercury intake of the pore A in thenegative active material layer increase, the diameter and thecorresponding differential mercury intake of the pore B decrease, the OIvalue increases, and the gram capacity increases, but the thicknessexpansion rate is affected.

Table 3 shows how D go and D_(n10) of the negative active materialaffect the particle size ratio variation value(D_(1v50)−D_(2v50))/D_(1v50), the specific surface area (BET) growthrate, and the first-cycle Coulombic efficiency and the cycle thicknessexpansion rate of the lithium-ion battery. The negative active materialin Embodiments 17 to 32 are prepared from the negative active materialin Embodiment 11. By screening and grading the negative active materialin Embodiment 11, large particles and tiny particles in the negativeactive material are removed to adjust the particle size.

D_(1v50) is the powder size of the negative active material before beingpressed, and D_(2v50) is the powder size of the negative active materialafter being pressed under a pressure of 1 ton. B₁ is the specificsurface area of the negative active material before being pressed, andB₂ is the specific surface area of the negative active material afterbeing pressed under a pressure of 1 ton.

A method for exerting a pressure on the negative active material is:Putting 1.0±0.05 grams of negative active material powder onto a moldthat is 13 mm in diameter by using an electronic pressure tester(SUNSTEST UTM7305), exerting a pressure of 1 ton on the negative activematerial powder and keeping the pressure for 5 seconds, and thenremoving the powder after the pressure is relieved.

TABLE 3 (D_(1v50) − (B₂ − First- D_(2v50))/ B₁)/ cycle D_(v90) D_(n10)D_(v90)/ D_(1v50) D_(2v50) D_(1v50) × B₁ B₂ B₁ × coulombic ExpansionSerial number (μm) (μm) D_(n10) (μm) (μm) 100% (m²/g) (m²/g) 100%efficiency rate Embodiment 11 35.7 1.4 25.5 17.5 13.2 25% 1.25 2.31 85%90.0% 7.0% Embodiment 17 28.4 1.4 20.3 13.1 11.3 14% 1.35 2.16 60% 90.7%7.6% Embodiment 18 30.3 1.4 21.6 14.4 11.7 19% 1.33 2.23 68% 90.6% 7.5%Embodiment 19 32.1 1.4 22.9 15.6 12.1 22% 1.33 2.24 68% 90.4% 7.1%Embodiment 20 34.7 1.4 24.8 16.9 12.9 24% 1.31 2.28 74% 90.2% 6.8%Embodiment 21 28.4 4.1 6.9 13.2 11.3 14% 1.24 2.21 78% 91.1% 7.4%Embodiment 22 30.5 4.1 7.4 14.5 11.6 20% 1.19 2.15 81% 91.4% 7.3%Embodiment 23 32.2 4.1 7.9 15.7 12.1 23% 1.13 2.18 93% 91.6% 7.0%Embodiment 24 34.9 4.2 8.3 17.3 12.8 25% 1.12 2.16 93% 91.8% 6.7%Embodiment 25 28.5 6.8 4.2 13.5 11.4 16% 1.18 2.12 80% 91.3% 7.4%Embodiment 26 30.5 6.8 4.5 14.6 11.7 20% 1.11 2.01 81% 91.6% 6.9%Embodiment 27 32.2 6.9 4.7 15.9 12.3 23% 1.02 1.99 95% 91.5% 6.6%Embodiment 28 34.9 6.9 5.1 17.2 12.9 25% 0.96 1.93 101%  91.9% 6.5%Embodiment 29 28.8 9.2 3.1 13.7 11.5 16% 0.98 2.01 105%  91.5% 7.4%Embodiment 30 30.7 9.3 3.3 14.9 11.8 21% 0.94 1.99 112%  91.5% 7.0%Embodiment 31 32.3 9.4 3.4 16.0 12.2 24% 0.87 1.92 121%  91.6% 6.6%Embodiment 32 35.0 9.4 3.7 17.3 12.9 25% 0.80 1.92 140%  92.0% 6.5%

Comparison between Embodiments 17 to 20, embodiments 21 to 24,embodiments 25 to 28, and embodiments 29 to 32 shows that when D_(n10)remains constant and D_(v90) decreases, the particle size ratiovariation value (D_(1v50)−D_(2v50))/D_(1v50) decreases, the specificsurface area (BET) growth rate decreases, the first-cycle Coulombicefficiency increases, but the cycle thickness expansion rate increases.Comparison between Embodiments 17, 21, 25, and 29, Embodiments 18, 22,26, and 30, Embodiments 19, 23, 27, and 31, and Embodiments 20, 24, 28,and 32 shows that when D_(n10) increases, the number of tiny particlesin the negative electrode decreases, the specific surface area (BET)growth rate increases significantly, the first-cycle Coulombicefficiency improves significantly, and slight improvement is made inexpansion.

References to “embodiments”, “some embodiments”. “an embodiment”,“another example”. “example”, “specific example” or “some examples”throughout the specification mean that at least one embodiment orexample in this application includes specific features, structures,materials, or characteristics described in the embodiment(s) orexample(s). Therefore, descriptions throughout the specification, whichmake references by using expressions such as “in some embodiments”. “inan embodiment”, “in one embodiment”, “in another example”, “in anexample”, “in a specific example”, or “example”, do not necessarilyrefer to the same embodiment or example in this application. Inaddition, specific features, structures, materials, or characteristicsherein may be combined in one or more embodiments or examples in anyappropriate manner.

Although illustrative embodiments have been demonstrated and describedabove, a person skilled in the art understands that the aboveembodiments are not to be construed as a limitation on this application,and changes, replacements, and modifications may be made to theembodiments without departing from the principles, and scope of thisapplication.

What is claimed is:
 1. A negative electrode, comprising: a currentcollector and a negative active material layer disposed on the currentcollector, wherein the negative active material layer comprises negativeactive material particles, the negative active material particlescomprise secondary particles, the negative active material layercomprises a pore A, a diameter of the pore A is 59 nm to 73 nm whentested by a mercury intrusion porosimetry, and a ratio C004/C110 of thenegative active material layer is 6 to
 20. 2. The negative electrodeaccording to claim 1, wherein when tested by the mercury intrusionporosimetry, a differential mercury intake of the pore A is 0.150 to0.190 mL/g·μm⁻¹.
 3. The negative electrode according to claim 1, whereinthe negative active material laver comprises a pore B, and, when testedby the mercury intrusion porosimetry, a diameter of the pore B is 66) nmto 800 nm, and a differential mercury intake of the pore B is 0.160 to0.230 mL/g·μm⁻¹.
 4. The negative electrode according to claim 3, whereina volume ratio between the pore B and the pore A is 0.7:1 to 1.42:1. 5.The negative electrode according to claim 1, wherein the negative activematerial particles satisfy at least one of conditions (a) to (d): (a)D_(v50) of the negative active material particles is 7.2 to 21.6 μm; (b)D_(v90) of the negative active material particles is 28.4 to 40.0 μm;(c) D_(n10) of the negative active material particles is 1.4 to 9.4 μm;or (d) D_(v90) and D_(n10) of the negative active material particlessatisfy: D_(v90)/D_(n10)≤26.
 6. The negative electrode according toclaim 1, wherein a powder particle size of the negative active materialparticles before being pressed is D_(1v50), a powder particle size ofthe negative active material particles after being pressed under apressure of 1 ton is D_(2v50), and(D_(1v50)−D_(2v50))/D_(1v50)×100%≤25%.
 7. The negative electrodeaccording to claim 1, wherein a specific surface area of the negativeactive material particles is 0.8 to 2.0 m²/g.
 8. The negative electrodeaccording to claim 1, wherein a specific surface area of the negativeactive material particles before being pressed is B₁, a specific surfacearea of the negative active material particles after being pressed undera pressure of 1 ton is B₂, and (B₂−B₁)/B₁×100%≤140%.
 9. Anelectrochemical device, comprising a positive electrode, a negativeelectrode, a separator, and an electrolytic solution; the negativeelectrode comprising a current collector and a negative active materiallayer disposed on the current collector, wherein the negative activematerial layer comprises negative active material particles, thenegative active material particles comprise secondary particles, thenegative active material layer comprises a pore A, a diameter of thepore A is 59 nm to 73 nm when tested by a mercury intrusion porosimetry,and a ratio C004/C110 of the negative active material layer is 6 to 20.10. The electrochemical device according to claim 9, wherein when testedby the mercury intrusion porosimetry, a differential mercury intake ofthe pore A is 0.150 to 0.190 mL/g·μm⁻¹.
 11. The electrochemical deviceaccording to claim 9, wherein the negative active material lavercomprises a pore B, and, when tested by the mercury intrusionporosimetry, a diameter of the pore B is 660 nm to 800 nm, and adifferential mercury intake of the pore B is 0.160 to 0.230 mL/g·μm⁻¹.12. The electrochemical device according to claim 11, wherein a volumeratio between the pore B and the pore A is 0.7:1 to 1.42:1.
 13. Theelectrochemical device according to claim 9, wherein the negative activematerial particles satisfy at least one of conditions (a) to (d): (a)D_(v50) of the negative active material particles is 7.2 to 21.6 μm; (b)D_(v90) of the negative active material particles is 28.4 to 40.0 μm;(c) D_(n10) of the negative active material particles is 1.4 to 9.4 μm;or (d) D_(v90) and D_(n10) of the negative active material particlessatisfy: D_(v90)/D_(n10)≤26.
 14. The electrochemical device according toclaim 9, wherein a powder particle size of the negative active materialparticles before being pressed is D_(1v50), a powder particle size ofthe negative active material particles after being pressed under apressure of 1 ton is D_(2v50), and(D_(1v50)−D_(2v50))/D_(1v50)×100%≤25%.
 15. The electrochemical deviceaccording to claim 9, wherein a specific surface area of the negativeactive material particles is 0.8 to 2.0 m²/g.
 16. The electrochemicaldevice according to claim 9, wherein a specific surface area of thenegative active material particles before being pressed is B₁, aspecific surface area of the negative active material particles afterbeing pressed under a pressure of 1 ton is B₂, and (B₂−B₁)/B₁×100%≤140%.17. The electrochemical device according to claim 9, wherein when theelectrochemical device is discharged to a voltage of 3 V, a specificsurface area of the negative active material particles is 1.5 to 2.4m²/g.
 18. The electrochemical device according to claim 9, wherein whenthe electrochemical device is charged to a voltage of 4.45 V, as testedby a differential scanning calorimetry (DSC), a maximum exothermic peakof the negative active material layer is 280 to 330° C.
 19. Theelectrochemical device according to claim 9, wherein the electrochemicaldevice satisfies at least one of conditions (e) or (f): (e) when theelectrochemical device is discharged to a voltage of 3 V, a powderparticle size of the negative active material particles is D_(av50), apowder particle size of the negative active material particles afterbeing pressed under a pressure of 1 ton is D_(bv50), and(D_(av50)−D_(bv50))/D_(av50)×100%≤2%; (f) when the electrochemicaldevice is discharged to a voltage of 3 V, a specific surface area of thenegative active material particles before being pressed is B₁₁, aspecific surface area of the negative active material particles afterbeing pressed under a pressure of 1 ton is B₂₂, and(B₂₂−B₁₁)/B₁₁×100%≤40%.
 20. An electronic device, comprising anelectrochemical device, the electrochemical device comprising a positiveelectrode, a negative electrode, a separator, and an electrolyticsolution, the negative electrode comprising a current collector and anegative active material layer disposed on the current collector,wherein the negative active material layer comprises negative activematerial particles, the negative active material particles comprisesecondary particles, the negative active material layer comprises a poreA, a diameter of the pore A is 59 nm to 73 nm when tested by a mercuryintrusion porosimetry, and a ratio C004/C110 of the negative activematerial layer is 6 to 20.